This invention relates to the processing of reflected, or echo, signals obtained by the use of signal transmitter-receiver equipment and has particular applications in the fields of hydro-acoustic transceivers, such as sonar equipment, echo sounders, and medical acoustics, and the field of radar, especially marine radar.
The terms transceiver and transmitter-receivers when used herein are intended to mean equipment for transmitting pulses and for receiving consequent echoes of the transmitted pulses, and is not limited, unless it is otherwise expressly stated, by the type of pulse (e.g. it may be sonic, supersonic or electromagnetic) nor is it limited to equipment which shares transmitting and receiving parts.
In the field of sonic and supersonic waves, equipment is available, such as sonar and echo sounders, which gives audible and visible indications of the existence of return echoes. Echo sounders, for example, give results recorded on recording paper.
In order to improve such equipment, circuitry has been designed for processing the return echo signal in order to extract from it more information than has heretofore been readily available with this type of equipment. Such a circuit is shown in U.K. specification No. 8221670 in which means are provided to extract the second bottom echo component of the return echo signal in order to provide information about the nature of the seabed. In that specification, it was disclosed that the nature of the seabed was revealed by sensing whether or not the second bottom echo component had an amplitude above a preset threshold level.
It has now been discovered that further useful information is present in the return echoes of equipment such as echo sounders and that this information can also be present in the return echoes of sonar, radar, medical ultrasonics and transceivers generally.
In particular, it has been discovered that information resides not just in the timing and size of a return pulse but also in its shape. Owing to saturation effects, such information is normally not available in the return echo of high power equipment. When lower transmitted power is employed, it has now been found that return echoes have shapes depending upon the nature of the reflecting surface or surfaces, for example seabed layers as is pertinent in surveying and sub-bottom profiling.